This invention relates to reinforced steel beams used in the construction of buildings and bridges.
Buildings and bridges are commonly made of steel beams and girders upon which a floor or road surface is laid. The beams and girders are selected from standard rolled sections. Or, they are designed to have enough material in the compression and tension flanges to resist the stress of the load (bending) moment, with an acceptable amount of deflection in the beam at the location of the maximum moment. When a load is placed upon the floor or road surface, the load creates a downward or bending moment which bends the steel beams downwardly. The downward moment places the top of the beam in compression and the bottom of the beam under tension. This load may ultimately cause the beams to fail at some point in the future. By compressing the bottom of the beam, the designer is able to counter-act and reduce the bending effect of the load moment, which will also reduce the horizontal shear in a loaded beam or girder. Counter-acting the load (bending) moment may also aid in the beam's ability to resist the effects of, for example, an earthquake. The life of the beams and the load they can carry can thus be increased by reinforcing the beam so as to produce an upward, or counter, moment in the beam, to counteract the downward moment created by the load placed on the beam.
Various methods have been used to reinforce steel beams. One method of reinforcing beams, such as I-beams or T-beams, involves securing steel plates to the beam. This provides the extra strength to the beam; however, it increases the weight of the beam. The steel content of a building is one of its most costly components. Thus, the extra steel used in the construction of buildings using this method drastically increases the cost of the building.
Mauquoy U.S. Pat. No. 4,006,523 describes a method of pre-stressing a steel beam that avoids the use of plating the beam. Mauquoy secures a plurality of varying length transmission elements to the bottom of the beam. Guides and wires are then secured to the transmission elements. The wires extend around the guides. The wires are then stressed to provide an upward moment to the beam to counteract the load. However, before the wires are stressed, supports are placed above and below the beam to compress the beam, to induce an upward moment in the beam. The wires are then tensioned, and the wires, transmission elements, and guides are then encased in concrete to hold the tension in the wires. Mauquoy's method requires special machinery to provide the upward moment to the beam. The beams cannot, thus, be reinforced on the building site. Further, the concrete adds a great amount of weight to the beam. This, again, significantly increases the ultimate weight of the building, and significantly adds to its construction cost.
Kandall U.S. Pat. No. 3,427,773 discloses a method of pre-stressing a beam which does not use concrete. Kandall teaches pre-stressing the beam by securing stiffener plates to the vertical web of the beam and then anchoring a cable or tendon to the beam along its vertical web. Kandall secures the cable to the beam at several locations so the cable lies along a polygonal line. Kandall's construction requires extra steel to produce the stiffeners. Further, because the stiffeners extend the length of the beam's vertical web, holes must be drilled therethrough to allow the cable to pass from one end of the beam to the other. This reinforcing system also causes substantial interference with the framing of other beams into the beam being reinforced. Kandall's method further adds significant weight to the beam and is complex and costly to use.